The invention is generally related to the field of data processing systems, and more particularly to data processing systems employing data storage distributed across geographically separated locations.
Distributed storage systems are known in which physical storage resources such as disk drives are distributed across two or more geographically separated locations. Each location includes one or more caching storage controllers connected to the local disk drives, for example by a storage-area network (SAN), and the caching storage controllers of the different locations are connected together by a wide-area communications network. The caching storage controllers are standalone hardware units also having connections to local host computers which utilize the storage resources provided by the caching storage controllers. The connections to the local host computers may also be via a SAN or other storage-oriented interconnect (e.g., Fibrechannel), and typically involve use of a storage-oriented protocol such as SCSI. A storage controller parses SCSI commands received from the separate host computers and performs corresponding storage operations on local and/or remote disk drives.